RU2585155C2 - Method for diagnosing oxidation catalyst for measuring level of nitrogen oxide after device for selective catalytic reduction - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to method of diagnostics of oxidation catalyst in gas discharge line. Diagnostic technique for oxidation catalyst (40) in line (20) of exhaust gases (90), leaving internal combustion engine (80), wherein discharge line (20) has device for selective catalytic reduction (60) located behind oxidation catalyst (40), relative to direction of exhaust gases. Method involves measurement of level of nitrogen oxides for selective catalytic reduction device (60) relative to direction of exhaust gases (90), which is only NOx transducer arranged for selective catalytic recovery device; establishment of failure of oxidation catalyst (40) depending on the measured level of nitrogen oxides, wherein failure of oxidation catalyst (40) is set when measured level of nitrogen oxides exceeds threshold level of nitrogen oxides, predetermined as failure oxidation catalyst (40); alarm on failure of oxidation catalyst (40).

EFFECT: technical result is more effective diagnosis of failure of cleaning mechanism.

12 cl, 7 dwg

Description

The present invention claims the priority of French patent applications 1151675 and 1151676 dated March 2, 2011, the contents of which (text, drawings and claims) are hereby incorporated by reference.

The present invention relates to a method for diagnosing an oxidation catalyst in an exhaust gas line leaving an internal combustion engine. The invention also relates to a vehicle comprising an exhaust line and a computer using the above method.

In the automotive industry, critical issues are reducing fuel consumption and reducing air emissions.

Thus, carbon monoxide (abbreviated as CO) and hydrocarbons (abbreviated as HC) are pollutants that seek to reduce emissions into the atmosphere. To reduce the amount of these pollutants, oxidation catalysts are known to be used. Such an oxidation catalyst is also known under the abbreviation CatOx or the English expression Diesel Oxydation Catalyst (Diesel Oxidation Catalyst), abbreviated DOC. Hereinafter, the abbreviation “DOC” and the term “oxidation catalyst” are used interchangeably.

In addition, other pollutants are nitrogen monoxide (NO), nitrogen dioxide (NO ₂ ) and nitrous oxide (N ₂ O), commonly known as NO _x . Note that DOC does not contribute to a complete decrease in NO _x emission, since DOC, due to its oxidizing properties, catalyzes the formation of nitrogen dioxide from nitrogen monoxide. Thus, DOC contributes to an increase in the ratio of nitrogen dioxides to nitrogen oxides; this ratio is hereinafter designated NO ₂ / NO _x .

Therefore, it is especially useful to provide a special device for removing nitrogen dioxide and, in particular, all nitrogen oxides. The agents commonly used to eliminate these gases are selective catalytic reduction devices (in English, Selective Catalytic Reduction, abbreviated SCR), combined with the introduction of urea or NH ₃ . Hereinafter, the abbreviation "SCR" and the term "selective catalytic reduction" are used interchangeably.

Thus, the DOC and the SCR device are classically integrated in the exhaust line of the gas leaving the internal combustion engine. FIG. 1 and 2 show examples of exhaust lines 20 connected to an internal combustion engine 80. These exhaust lines 20 may include a DOC 40 and an SCR 60 arranged in that order with respect to the gas discharge direction 90.

To ensure the time efficiency of the cleaning mechanisms located in the exhaust line 20, various methods have been proposed for diagnosing the failure of these mechanisms. It is known, for example, to use temperature sensors to determine the exothermic effect of DOC. It is also known to use molecular oxygen level sensors to detect a change in molecular oxygen consumption by a DOC catalyst. Determining the exothermic effect or determining the change in molecular oxygen flow rate allows you to diagnose DOC failure. Alternatively, documents WO2008 / 093616 A, WO2009 / 101728 A and DE 10328856 A describe methods for diagnosing DOC failure by measuring the NO _x level at the output of the DOC and, optionally, before the DOC. Thus, each known diagnostic method proposes to use a special sensor to detect DOC failure. The use of a special sensor leads to a more complex and, therefore, in particular, more expensive exhaust line.

The first type of methods is based on modeling the operating parameters of the exhaust line to diagnose the failure of the exhaust line. Thus, document WO2010 / 113269 A proposes an estimated calculation of the NO ₂ level in an exhaust line to establish a line failure. Since the real values of the operating parameters of the exhaust line are not determined in this first type of methods, the reliability of such methods leaves much to be desired.

Methods of the second type are based on measuring the actual values of the operating parameters of the exhaust line. Documents WO2008 / 093616 A, WO2009 / 101728 A and DE 10328856 A describe, for example, methods for diagnosing DOC failure by measuring the NO _x level at the DOC output and possibly before the DOC. Thus, the second type of diagnostic methods suggest using a special sensor to detect DOC failure. However, the use of a special sensor leads to a more complex and, in particular, more expensive exhaust line.

Thus, there is a need for a reliable method for diagnosing a failure of the cleaning mechanism in the exhaust line, while the simplicity of the design of the exhaust line should be maintained, and in particular, there is a need for a method for diagnosing an oxidation catalyst that can be carried out in a simpler exhaust line.

To this end, the invention provides a method for diagnosing an oxidation catalyst in a gas exhaust line leaving an internal combustion engine, the exhaust line comprising a selective catalytic reduction device located, in the gas discharge direction, behind the oxidation catalyst, the method comprising:

- measuring the level of nitrogen oxides behind the selective catalytic reduction device, in the direction of the exhaust gas, and

- determination of the failure of the oxidation catalyst, depending on the measured level of nitrogen oxides.

According to one embodiment, it is determined that the oxidation catalyst has failed when the measured level of nitrogen oxides falls below the threshold level of nitrogen oxides, predetermined as the failure of the oxidation catalyst.

According to one embodiment, the method includes, based on the measured level of nitrogen oxides, calculating the degree of conversion of nitrogen oxides in the selective catalytic reduction device, wherein the oxidation catalyst failure is established when the conversion degree of the selective catalytic reduction device falls below a threshold degree of conversion predetermined as oxidation catalyst failure.

According to one embodiment, the method includes:

- measuring the level of carbon monoxide or the level of hydrocarbons before the selective catalytic reduction device and behind the oxidation catalyst, relative to the direction of release of gases, and

- determination of the failure of the oxidation catalyst when the measured level of carbon monoxide or hydrocarbons exceeds the threshold level of carbon monoxide or hydrocarbons, predetermined as the failure of the oxidation catalyst.

According to one embodiment, the method includes:

- measuring the ratio of nitrogen dioxides to nitrogen oxides, before the selective catalytic reduction device and behind the oxidation catalyst, in the direction of exhaust gases, and

- establishing the failure of the oxidation catalyst when the measured ratio of nitrogen dioxide to nitrogen oxides falls below the threshold value of the ratio of nitrogen dioxide to nitrogen oxides, predetermined as the failure of the oxidation catalyst.

According to one embodiment, the method includes:

- measuring the flow rate of molecular oxygen by the oxidation catalyst, and

- establishing the failure of the oxidation catalyst when the measured flow rate falls below the threshold molecular oxygen flow rate, predetermined as the failure of the oxidation catalyst.

According to one embodiment, the method includes:

- measuring or evaluating the exothermic effect created by the oxidation catalyst, and

- determination of the failure of the oxidation catalyst, depending on the measured or estimated exothermic effect.

According to one embodiment, the method further comprises introducing urea prior to the selective catalytic reduction device, in the direction of the gas discharge.

According to one embodiment, the internal combustion engine from which the gases emitted by the exhaust line exit is a diesel engine.

In one particular embodiment of the above method, the invention also provides a method for diagnosing a device failure in a gas exhaust line leaving an internal combustion engine, the exhaust line comprising, in the gas discharge direction, an oxidation catalyst and a selective catalytic reduction device, and the method includes:

- measurements at the first temperature and at the second temperature of the level of nitrogen oxides behind the selective catalytic reduction device, in the direction of exhaust gases, and the second temperature is higher than the first temperature, and

- determination of the failure of the oxidation catalyst when:

- at the first temperature, the measured level of nitrogen oxides corresponds to the functional insufficiency of the selective catalytic reduction device, and when

- at the second temperature, the measured level of nitrogen oxides does not correspond to the functional insufficiency of the selective catalytic reduction device.

In one embodiment, at least one of the first and second temperatures is a temperature measured at the level of a selective catalytic reduction device.

According to one embodiment, at least one of the first and second temperatures is a design temperature in a selective catalytic reduction device, the evaluation being made from a temperature model in the discharge line.

According to one embodiment, the temperature model is based on at least one of the parameters of a group of parameters consisting of:

- engine operating mode,

- engine torque

- fuel consumption by the engine,

- phasing fuel injection into the engine,

- air flow rate of the engine,

- the degree of return to the engine of the exhaust gas from the exhaust line,

- valve system at the engine inlet,

- the speed of the vehicle containing the engine and the exhaust line, and

- the position of the turbocharger at the inlet of the engine, taking the kinetic energy of the gas emitted into the exhaust line.

According to one embodiment, the method includes determining the failure of the selective catalytic reduction device when, at the first temperature and at the second temperature, the measured level of nitrogen oxides corresponds to the functional failure of the selective catalytic reduction device.

According to one embodiment, at least at one of the first and second temperatures, the measured level of nitrogen oxides corresponds to the functional failure of the selective catalytic reduction device when the measured level of nitrogen oxides exceeds the threshold level of nitrogen oxides, predetermined as failure.

According to one embodiment, at least at one of the first and second temperatures, the method includes calculating the degree of conversion of nitrogen oxides in the selective catalytic reduction device based on the measured level of nitrogen oxides, wherein the measured level of nitrogen oxides at least one of the first and second temperatures corresponds to functional insufficiency of the selective catalytic reduction device, when the calculated degree of conversion of nitrogen oxides becomes lower than the threshold degree of conversion, pr dopredelennoy as a failure.

According to one embodiment:

- the first temperature is the temperature of the normal operation of the exhaust line and ranges from 150 ° C to 300 ° C, and

- the second temperature is the elevated temperature of the exhaust line and is greater than or equal to 300 ° C.

According to one embodiment, applicable to all embodiments of the method of the invention, the internal combustion engine from which the gases emitted to the exhaust line exit is a diesel engine.

The invention also provides an automobile comprising an internal combustion engine, a gas exhaust line of an internal combustion engine and an exhaust line diagnostics computer, the exhaust line comprising, in the direction of exhaust gases, an oxidation catalyst, a selective catalytic reduction device, a nitrogen oxide level sensor and a computer in which the above diagnostic method in any of the embodiments.

Other characteristics and advantages of the invention will emerge from a study of the following detailed description of embodiments of the invention, given solely as an example, when referring to the drawings, which show:

- FIG. 1 and 2: a schematic representation of exhaust lines connected to an internal combustion engine;

- FIG. 3: a graph comparing the change in the ratio of nitrogen dioxide to nitrogen oxide for the new and old oxidation catalysts;

- FIG. 4: a graph of the processing efficiency of nitrogen oxides in the exhaust line of FIG. 1 or 2 depending on the temperature and the ratio of nitrogen dioxide to nitrogen oxide;

- FIG. 5: a graph showing the total emission of pollutants emanating from various oxidation catalysts, depending on different thresholds predetermined as failure of the oxidation catalyst;

- FIG. 6: a histogram of the processing efficiency of nitrogen oxides in the exhaust line of FIG. 1 depending on the ratio of nitrogen dioxide to nitrogen oxide at the first and second temperature;

- FIG. 7: a graph comparing temperature changes for new and old catalysts.

A method for diagnosing an oxidation catalyst is provided. It is envisaged that the diagnostics will be carried out in the exhaust line of gases leaving the internal combustion engine. The internal combustion engine is preferably a diesel engine. To illustrate the placement of the DOC 40 in the exhaust line 20, refer to the above-described FIG. 1 and 2.

According to FIG. 1 and 2, and according to the first embodiment, the exhaust line 20, where the proposed method is implemented, comprises a selective catalytic reduction device 60 behind the DOC 20 in the direction of gas discharge. Hereinafter, the use of the terms “for” and “before” defines in the exhaust line 20 the position of one device relative to another device with respect to the direction of gas exit to the exhaust line 20.

The method includes measuring the level of nitrogen oxides behind the SCR 60 device. The method further includes determining the failure of the DOC 40 catalyst.

Indeed, of the known failures of the DOC 40, aging of the DOC 40 results, in particular, in a decrease in the oxidation efficiency of HC and CO and a decrease in the NO ₂ / NO _x ratio behind the DOC 40. FIG. 3 shows a graph comparing the change in the NO ₂ / NO _x ratio for fresh DOC 40 (curve 70) and for old DOC 40 (curve 72). The change in the NO ₂ / NO _x ratio for each DOC 40 is associated with the same standard operating program of the internal combustion engine 80. Thus, FIG. 3 shows the change in speed of the engine 80 when the engine 80 is subjected to a standard operating program (curve 78).

However, a decrease in the NO ₂ / NO _x ratio for DOC 40 entails an increase in NO _x emission behind the SCR 60 due to the worse SCR efficiency. This decrease in SCR efficiency is seen on surface 76 in FIG. 4, which shows a graph of the NO _x processing efficiency in the exhaust line 80 versus the NO ₂ / NO _x ratio.

Thus, from a decrease in SCR efficiency due to a decrease in the NO ₂ / NO _x ratio, a decrease in DOC 40 activity can be established by measuring the NO _x level behind the SCR 60. The failure of the DOC 40 depending on the NO _x level behind the SCR 60 can be set in accordance with at least one of the following two options.

A DOC 40 failure can be detected, for example, when the measured level of nitrogen oxides exceeds a threshold level of nitrogen oxides, predetermined as a failure of DOC 40.

DOC 40 failure can also be established by calculating the NO _x conversion rate in the SCR 60 device. The NO _x conversion rate in the SCR 60 device is calculated based on the measured NO _x level and NO _x level to the SCR 60 device. NO _x level to the SCR 60 device can be determined using a special sensor or using a model for calculating the NO _x level to the SCR 60 device. Thus, the NO _x level to the SCR 60 device is measured or evaluated and allows, together with the NO _x level measured downstream, to calculate the degree of NO conversion _x in the unit SCR 60. When carried out calculating the degree of NO _x conversion in the SCR device 60, the rejection DOC 40 is set when the calculated degree of conversion becomes less than the threshold degree of conversion, DOC 40 as the predetermined failure.

Both of the above options for establishing the failure of the DOC 40 can be used simultaneously on the exhaust line 20.

In other words, in all cases, the proposed method makes it possible to diagnose a DOC 40 failure not directly by reducing the cleaning efficiency of HC and CO, but indirectly by NO _x emission behind the SCR 60 device.

However, according to FIG. 1 and 2, the NO _x 64 sensor behind the SCR is equipped with an on-board NO _x reduction diagnostics computer (not shown), the on-board NO _x reduction diagnostics computer has an integrated computer, better known as an OBD computer (short for English expression "on board diagnostics "- on-board diagnostics).

Implementation of the proposed method with the same built-in computer does not entail the need for an additional sensor, unlike other known solutions, such as DOC 40 diagnostics by the exothermic effect of DOC 40 or by changing the oxygen flow rate of the DOC 40 catalyst. Thus, without requiring an additional sensor, the exhaust line 20, for which the proposed diagnostic method is applied, is simpler.

As a result, the proposed method for diagnosing an oxidation catalyst can be applied on a simpler exhaust line.

The threshold level NO _x , predetermined as a failure of the DOC 40, may correspond to the threshold value stored in the computer memory OBD. This predefined threshold level is part of the regulatory levels for various HC, CO or NO _x pollutants.

FIG. 5 shows a graph illustrating the total emission of HC, CO, or NO _x pollutants depending on different predefined DOC 40 failure thresholds. The threshold value 94 corresponds to the CO threshold value predetermined as the DOC 40 failure. The threshold value 96 corresponds to the threshold level of NO _x and non-methane HC (abbreviated NMHC), predefined as failure of DOC 40. FIG. 5 shows the total emissions of HC, CO, or NO _x pollutants that come from oxidation catalysts of various technologies: DOC 1, DOC 2, DOC 3, DOC 4 and DOC 5, and to which the standard work program has been applied. For each of these DOCs, exceeding a predetermined threshold value of 96 for NO _x occurs before exceeding a predetermined threshold value of 94 for CO and non-methane HC. Thus, the proposed diagnostic method can detect the failure of DOC 40 and prevent the excessive release of other regulated pollutants, such as CO, for different DOC technologies.

In addition, for reasons of reliability of the detection method, this method may further include measuring the CO level or HC level before the SCR 60 and behind the DOC 40 catalyst. The result of this measurement, when it exceeds the threshold CO or HC level, predetermined as a DOC 40 failure, allows additional DOC 40 failure detection, which is beneficial. According to this embodiment, the discharge line 20 may then be provided with an additional sensor.

For the same purpose, the reliability of the proposed diagnostic method, the method may also include measuring the NO ₂ / NO _x ratio before the SCR 60 device and beyond the DOC 40. The result of this measurement, when it falls below the threshold value of NO ₂ / NO _x , predetermined as DOC 40 failure, allows a better determination of DOC 40 failure, which is beneficial. According to this embodiment, the discharge line 20 may then be provided with an additional sensor.

Again, for reliability purposes, the method may further include measuring or evaluating the degree of conversion of NO _x to NO ₂ on the DOC 40 catalyst. The result of this measurement or this estimate, when it falls below the threshold degree of conversion characterizing the DOC failure, allows better failure of DOC 40, which is beneficial. According to this embodiment, the discharge line 20 may then be provided with an additional sensor.

Also for this reliability purpose, the method may include, in addition, measuring the O ₂ flow rate of the DOC 40 catalyst. The result of this measurement, when it falls below the threshold value of the O ₂ flow rate, predetermined as the DOC 40 failure, allows better determination of the DOC 40 failure, which is beneficial. According to this embodiment, the discharge line 20 may then be provided with an additional sensor.

For the same purpose of reliability, the method may also include measuring or evaluating the exothermic effect of the DOC 40. The result of this measurement or this assessment, when it does not correspond to the threshold value predetermined as the failure of the DOC 40, allows a better determination of the failure of the DOC 40, which is beneficial. Mismatch of the exothermic effect to a threshold value predetermined as failure can mean a decrease in the exothermic effect of the DOC 40 catalyst due to its aging. Thus, it is possible to better determine the failure of the DOC 40 when the measured or calculated exothermic effect of the DOC 40 falls below the threshold temperature predefined as the failure of the DOC 40. Non-compliance of the exothermic effect with the threshold predetermined as the failure can also mean a decrease in the temperature rise of the DOC 40 during exhaust operation line 20. Thus, a better determination of the failure of the DOC 40 is possible when the rate of increase in temperature of the DOC 40 falls below the threshold temperature increase, predetermined as DOC 40 failure. According to whether the exothermic effect is measured or evaluated, the exhaust line 20 may be equipped with an additional sensor.

According to FIG. 1 and 2, the exhaust line 20 may comprise a urea injector 62 prior to the SCR 60 device. Thus, the proposed method may also include introducing urea prior to the SCR 60 device. Urea corresponds to a reducing agent in the SCR reaction, also known as AUS32 (aqueous urea solution 32, 5%).

The invention also relates to a car. The vehicle comprises an internal combustion engine 80, a gas exhaust line 20 from the internal combustion engine 80, and a diagnostic computer for the exhaust line 20 described above. Referring to FIG. 1 and 2, the exhaust line 20 also includes a NO _x level sensor 64. The computer preferably implements the above diagnostic method. Implementation of the above diagnostic method for the exhaust line 20 is possible, although the exhaust line 20 may not contain sensors between the DOC 40 and the SCR device 60.

The proposed method preferably includes a DOC 40 failure alarm. This alarm is then intended for a driver of a vehicle having an exhaust line 20, or for a person using an internal combustion engine 80.

In view of FIG. 1, 3, 4, 6 and 7, another embodiment of the method according to the invention is described, while the characteristics common to the two options are not repeated for brevity. A method for diagnosing a device failure in an exhaust line is proposed. It is envisaged that the diagnosis is carried out in the exhaust line of gases leaving the internal combustion engine. The internal combustion engine is preferably a diesel engine. To illustrate the placement of the DOC 40 and the selective catalytic reduction device 60 in the exhaust line 20, refer to the above-described FIG. one.

The method includes measuring the level of nitrogen oxides behind the SCR 60. These measurements of the NO _x level are carried out at the first temperature T1 and at the second temperature T2. T2 is higher than T1. Indeed, T1 may correspond to a low or medium operating temperature of the exhaust line 20, while T2 may correspond to an elevated operating temperature of the exhaust line 20. Then T1 preferably corresponds to a temperature of 150 ° C to 300 ° C, and T2 preferably corresponds to a temperature greater than or equal to 300 ° C.

The method further includes determining the failure of DOC 40.

So, to reduce the SCR efficiency due to a decrease in the NO ₂ / NO _x ratio at low and medium temperatures, it is possible to establish a failure in the exhaust line by measuring the NO _x level behind the SCR 60 at temperature T1.

However, it may be useful to distinguish which device failed, the DOC 40, or the SCR 60 device.

In the case where the DOC 40 fails while the exhaust line 20 experiences an elevated temperature, a decrease in the NO ₂ / NO _x ratio behind the DOC 40 due to the failure does not entail a significant decrease in the NO _x processing efficiency of the SCR 60. Indeed, according to FIG. 3, the reduction in NO _x processing efficiency of the SCR 60 is much less at elevated temperatures of the SCR 60 than at low and medium temperatures in the SCR 60. FIG. 6 shows a histogram of the NO _x processing efficiency versus the NO ₂ / NO _x ratio at T1 and T2. This histogram also reveals that the reduction in NO _x processing efficiency as a function of the NO ₂ / NO _x ratio is not significant at either T1 or T2. Thus, at ordinary temperatures (T1), the NO _x processing efficiency in the SCR 60 device depends on the NO ₂ / NO _x ratio, and at elevated temperatures (T2) this no longer takes place.

In contrast, in the case where the SCR device fails, the NO _x processing efficiency is reduced behind the SCR 60 regardless of the temperature in the SCR 60.

In other words, DOC failure can be detected when:

- at the first temperature T1, the measured level of NO _x corresponds to the functional failure of the SCR 60, and when

- at the second temperature T2, the measured level of NO _x does not correspond to the functional failure of the SCR 60 device.

When the measured NO _x level does not correspond to the functional failure of the SCR 60, this means that the measured NO _x level corresponds to the satisfactory operation of the SCR 60, that is, the normal operation of the SCR 60.

Determine whether or not the NO _x level measured behind the SCR 60 corresponds to the functional failure of the SCR 60 according to at least one of the following two options.

At a given temperature, T1 or T2, the functional failure of the SCR 60 may, for example, correspond to the case where the measured level of nitrogen oxides exceeds the threshold level of nitrogen oxides, predetermined as failure. The threshold level of nitrogen oxides, predetermined as failure, preferably depends on the temperature (T1 or T2) of the measurement of the NO _x level with which the threshold level is compared.

At a given temperature, T1 or T2, the functional failure of the SCR 60 can also be identified by calculating the degree of NO _x conversion in the SCR 60. The calculation of the NO _x conversion in the SCR 60 is based on the measured NO _x level and the NO _x level to the device SCR 60. The NO _x level to the SCR 60 device can be determined using a special sensor or using the NO _x level model to the SCR 60 device. The NO _x level to the SCR 60 device is thus measured or estimated and allows, together with the NO _x level measured behind the SCR 60, races read the NO _x conversion rate in the SCR 60 device. Thus, a functional failure may correspond to a reduction in the calculated NO _x conversion degree below the threshold conversion degree predetermined as failure. The threshold failure conversion rate preferably depends on the temperature (T1 or T2) of the NO _x level measurement from which the conversion rate is calculated.

Both of the above options for the correspondence between the measured level of NO _x and functional failure of the SCR 60 device can be used simultaneously in the proposed method. So, at a given temperature, the measured NO _x level may not correspond to the functional impairment of the SCR 60, when:

- the threshold level of NO _x , predetermined as a failure, remains above the measured level of NO _x , and / or

- the threshold degree of conversion, predetermined as failure, remains below the degree of conversion calculated from the measured level of NO _x .

In other words, the proposed method makes it possible to diagnose DOC 40 failure not directly, through a decrease in the processing efficiency of HC and CO, but indirectly through NO _x emissions behind the SCR 60 device.

Meanwhile, according to FIG. 1, the NO _x 64 sensor behind the SCR is equipped with an on-board NO _x reduction diagnostic computer (not shown). The on-board NO _x reduction diagnostic on-board computer is an integrated computer, better known as an OBD computer (short for the English expression “on board diagnostics” - on-board diagnostics).

Implementation of the proposed method by the same on-board computer does not entail the need for an additional sensor, in contrast to the known solutions. Thus, without requiring an additional sensor, the exhaust line 20, for which the proposed diagnostic method is applied, is simpler.

In addition, the measurement of NO _x behind the SCR device allows you to achieve greater reliability of the proposed method compared to the diagnostic method based on the estimated model of the level of NO _x behind the SCR device.

As a result, the invention provides a reliable method for diagnosing a failure of a treatment device in an outlet line, in which the outlet line retains a simple structure.

The invention also relates to a car. The vehicle includes an internal combustion engine 80, a gas exhaust line 20 from the internal combustion engine 80, and a diagnostic computer for the exhaust line 20 described above. According to figure 1, the exhaust line 20 also contains a sensor 64 level NO _x . The computer preferably implements the diagnostic method described above. The implementation of the above diagnostic method for the exhaust line 20 is possible even when the exhaust line 20 does not contain a sensor, in particular, an NO _x sensor between the DOC 40 and the SCR 60.

Different measurements of the NO _x level at T1 and T2 can be carried out at different phases of operation in the exhaust line 20 and engine 80. Thus, in one working phase at low or medium temperature, the first measurement of the level of NO _x at T1 can be written to the computer's memory. A second measurement of the NO _x level at T2 is performed when the exhaust line 20 and the engine 80 are in the phase of operation at elevated temperature.

When the exhaust line 20 contains at least one temperature sensor (not shown), the determination of the operating phases at low or medium temperature and at elevated temperature can be carried out by measurement. At least one of the temperatures T1 and T2 then corresponds to the temperature measured by the temperature sensor. Preferably, the temperature sensor was located in the exhaust line 20 for the implementation of other functions, and not only the diagnosis of failure, thereby reducing the cost of developing the exhaust line.

When there are no temperature sensors in the discharge line 20 at the level of the SCR 60, at least one of the temperatures at which the NO _x level is measured can be measured rather than measured. In this case, T1 and / or T2 correspond to the temperatures calculated at the time the NO _x level was measured for the SCR 60. The assessment in this case is based on the temperature model in the exhaust line 20. The temperature model used is preferably based on at least one of the group parameters parameters consisting of:

- engine operating mode 80,

- engine torque 80,

- fuel consumption by engine 80,

- phasing fuel injection into the engine 80,

- air flow by engine 80,

- the degree of return to the engine 80 of the exhaust gas 90 from the exhaust line 20,

- a valve system at the inlet of the engine 80,

- the speed of the vehicle containing the engine 80 and the exhaust line 20, and

- the position of the turbocharger at the inlet of the engine 80, which takes the kinetic energy of the gas 90 discharged into the exhaust line 20.

Thus, such a temperature model is based on parameters at engine level 80, which are classically used for other functions, and not for diagnosing exhaust line 20. Failure to achieve synergies that reduce development costs and complexity of engine 80, exhaust line 20, and the vehicle which contains them. In addition, this temperature model allows you to do without the special temperature sensor provided for measuring temperature in the SCR 60 device.

The proposed method may also make it possible to detect a failure of the SCR 60 when the levels of nitrogen oxides measured at T1 and T2 both correspond to the functional failure of the SCR. Indeed, in the event of failure of the SCR 60, the reduction in NO _x processing efficiency of the SCR 60 is significant, whatever the temperature in the SCR 60 is.

In other words, taking a measurement of the NO _x level at elevated temperatures (T2), when the SCR reaction is independent of the NO ₂ / NO _x ratio, and in addition, whether or not the result of this measurement shows the functional failure of the SCR 60, may raise questions. If the functional failure of the SCR 60 is no longer established at elevated temperatures (T2), then the SCR 60 is operating correctly, and thus the DOC 40 is compromised. If the functional failure of the SCR 60 is always detected at elevated temperatures (T2), then the SCR 60 device is at risk. Thus, the failure of the SCR 60 device can be established when the measured level of nitrogen oxides at T1 and at T2 exceeds each corresponding threshold level of nitrogen oxides, predetermined as failure T1 or T2. The failure of the SCR 60 can also be established when the NO _x conversion rate calculated from the NO _x contents measured at T1 and at T2 is each lower than the respective threshold degrees of conversion determined for failure at T1 or T2.

The distinction between a failure caused by a DOC 40 or caused by an SCR 60 device means that both devices are not required to be changed during servicing.

The proposed method preferably includes a failure alarm DOC 40 and / or SCR 60 device. In this case, this alarm is intended for the driver of the car containing the exhaust line 20, or for a person using the internal combustion engine 80. Because to distinguish the failure caused by the DOC 40 or caused SCR 60, it is possible on a running engine, the signaling of the source of failure can be indicated directly to the user immediately before going through service.

Once a reduction in the NO _x processing efficiency of measuring NO _x at ordinary temperatures (T1) has been established, an improvement in discrimination between the DOC 40 and the SCR 60 can be envisaged.

So, in the case where there are two temperature sensors in the exhaust line 20, before and behind the DOC 40, the method can blame the failure on the DOC 40 based on the exothermic effect it creates. Indeed, as the DOC 40 ages, the exothermic effect it creates is reduced. This decrease in exothermic effect can be seen in FIG. 7, which shows a graph comparing the change in temperature difference between points located before and behind the DOC 40 for the new DOC (54) and for the old DOC (56). The temperature difference curves 54 and 56 are obtained when the engine 80 is subjected to a standard operating program, shown by curve 58, corresponding to the speed of the vehicle containing the engine 80. It is also possible to assign responsibility to the DOC 40 based on the exothermic effect created by it by comparing the rate of increase in temperature of the DOC 40 with a given reference rate of temperature increase. The rate of increase in temperature of the DOC 40 decreases with aging of the DOC 40.

Assignment of responsibility to the DOC 40 on the basis of an exothermic effect can also be foreseen in the case when there is a single temperature sensor in the exhaust line 20. In this case, it is advantageous to place it at a known operating point to determine the reduction in the exothermic effect of DOC 40.

In the event that, in addition, temperature sensors are included in the exhaust line 20, the method may also include blaming the DOC 40 using the aging models of the DOC 40. Such a model consists in recording the temperature profile in the SCR 60 and in the DOC 40 during operation a car. Thus, failure can be attributed to a device whose aging, according to the model, will be greatest.

This method may also include blaming DOC 40 based on the consumption of O _{2 by the} DOC 40 catalyst. Indeed, as the DOC 40 ages, it consumes less oxygen used to treat pollutants. This responsibility is possible when an O ₂ sensor is installed in the exhaust line 20 to the DOC 40. However, the NO _x 64 sensor can also make it possible to determine the oxygen concentration, in particular if it is placed at a known operating point.

Claims (12)

1. A method for diagnosing an oxidation catalyst (40) in an exhaust gas line (90) (90) leaving an internal combustion engine (80), the exhaust line (20) comprising a selective catalytic reduction device (60) located behind the oxidation catalyst (40) ), relative to the direction of gas release, characterized in that it includes:
- measuring the level of nitrogen oxides behind the selective catalytic reduction device (60) with respect to the direction of gas discharge (90), which is carried out by a single NO _x sensor located behind the selective catalytic reduction device,
- determination of the failure of the oxidation catalyst (40) depending on the measured level of nitrogen oxides, and the failure of the oxidation catalyst (40) is established when the measured level of nitrogen oxides exceeds the threshold level of nitrogen oxides, predetermined as the failure of the oxidation catalyst (40),
- alarm about the failure of the oxidation catalyst (40). 2. The diagnostic method according to claim 1, characterized in that it includes, based on the measured level of nitrogen oxides, calculating the degree of conversion of nitrogen oxides in the selective catalytic reduction device (60), and the failure of the oxidation catalyst (40) is established when the degree of conversion to selective catalytic reduction device (60) becomes lower than the threshold degree of conversion, predetermined as the failure of the oxidation catalyst (40). 3. The diagnostic method according to p. 1, characterized in that it includes:
- measuring the level of carbon monoxide or the level of hydrocarbons before the selective catalytic reduction device (60) and behind the oxidation catalyst (40), relative to the direction of release of gases (90), and
- establishing the failure of the oxidation catalyst (40) when the measured level of carbon monoxide or hydrocarbons exceeds the threshold level of carbon monoxide or hydrocarbons, predetermined as the failure of the oxidation catalyst (40). 4. The diagnostic method according to p. 1, characterized in that it includes:
- measuring the flow rate of molecular oxygen by the oxidation catalyst (40), and
- establishing the failure of the oxidation catalyst (40) when the measured flow rate falls below the threshold molecular oxygen flow rate, predetermined as the failure of the oxidation catalyst (40). 5. The diagnostic method according to p. 1, characterized in that it includes:
- measuring or evaluating the exothermic effect created by the oxidation catalyst (40), and
- determination of the failure of the oxidation catalyst (40) depending on the measured or calculated exothermic effect. 6. The diagnostic method according to claim 1, characterized in that it comprises measuring at the first temperature (T1) and at the second temperature (T2) the level of nitrogen oxides behind the selective catalytic reduction device (60) in the direction of the gas outlet (90), the second the temperature (T2) is higher than the first temperature (T1), and the failure of the oxidation catalyst (40) is established when:
- at the first temperature (T1), the measured level of nitrogen oxides corresponds to the functional insufficiency of the selective catalytic reduction device (60), and when
- at the second temperature (T2), the measured level of nitrogen oxides does not correspond to the functional insufficiency of the selective catalytic reduction device (60). 7. The diagnostic method according to claim 6, characterized in that at least one of the first and second temperatures (T1, T2) is the temperature measured at the level of the selective catalytic reduction device (60). 8. The diagnostic method according to claim 6 or 7, characterized in that at least one of the first and second temperatures (T1, T2) is the calculated temperature in the selective catalytic reduction device (60), and the assessment is carried out according to the temperature model in the exhaust line (twenty). 9. The diagnostic method according to claim 8, characterized in that the temperature model is based on at least one of the parameters from the group of parameters consisting of: engine operation mode (80), engine torque (80), fuel consumption of the engine (80) , phasing the injection of fuel into the engine (80), the air flow rate of the engine (80), the degree of return to the engine (80) of the exhaust gas (90) from the exhaust line (20), the valve system at the engine inlet (80), the speed of the vehicle containing the engine (80) and the exhaust line (20), and the position of the turbocharger at the engine inlet of Tell (80), selects the kinetic energy of the gas (90) discharged into an exhaust line (20). 10. The diagnostic method according to claim 6, characterized in that it includes the failure of the selective catalytic reduction device (60), when at the first temperature (T1) and at the second temperature (T2) the measured level of nitrogen oxides corresponds to the functional insufficiency of the selective catalytic reduction device (60). 11. The diagnostic method according to claim 6, characterized in that at least at one of the first and second temperatures (T1, T2), the measured level of nitrogen oxides corresponds to the functional insufficiency of the selective catalytic reduction device (60), when the measured level of nitrogen oxides exceeds the threshold nitric oxide level, predetermined as failure. 12. The diagnostic method according to claim 6, characterized in that at least at one of the first and second temperatures (T1, T2), the method includes calculating the degree of conversion of nitrogen oxides in a selective catalytic reduction device (60) based on the measured level of nitrogen oxides moreover, the level of nitrogen oxides measured at at least one of the first and second temperatures (T1, T2) corresponds to the functional insufficiency of the selective catalytic reduction device (60), when the calculated degree of conversion of nitrogen oxides becomes camping below the threshold degree of conversion, predetermined as a failure.

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